Continually increasing demands are being made on an internal combustion engine, for example of a motor vehicle, in terms of reduced fuel consumption and exhaust emissions, while greater output is also desired. To meet these demands, modern internal combustion engines are equipped with a fuel supply system in which the delivery of fuel into the combustion chamber of the internal combustion engine is controlled and/or regulated electronically, in particular by means of a computer-aided control device. It is possible in this context to inject the fuel into an air intake pipe of the internal combustion engine, or directly into the combustion chamber of the internal combustion engine.
With the latter method in particular, which is referred to as "direct injection," the fuel must be injected under pressure into the combustion chamber. Provided for this purpose is a pressure accumulator into which the fuel is pumped by means of a pump and subjected to a high pressure. From there the fuel is then injected through injection valves into the combustion chambers of the internal combustion engine.
A number of operating states can occur while the internal combustion engine is in operation. At full load, the internal combustion engine produces its maximum output; at part load it produces a desired portion thereof. At idle, the rotation speed of the internal combustion engine is as low as possible. And in coastdown (overrun) mode, the internal combustion engine generates no output, but instead creates a certain braking action.
Coastdown mode occurs, for example, when the motor vehicle is traveling down a sloping road and the driver of the motor vehicle removes his or her foot from the accelerator pedal. As a result, no further fuel is injected into the internal combustion engine, and often, in addition, no further air is delivered to the internal combustion engine. The injection valves thus remain closed during a coastdown period of this kind. Thus not only is the desired braking effect achieved, but also fuel is thereby saved.